[Rescue Toaster]

Hey sbelyo, nice work.

Couple questions, you have no extra resistors in the power supply yet, right? What voltage do you get on top of the 6as7's? Close to 170v? What is the voltage on the cathode of the 6as7's? (ie how much current are they passing)

Drew a little picture for you of what I meant, though I think you got it. You could even do totally separate L & R star grounds, and run separate wires from the power supply star ground to each. But... I don't think it's a big issue and you'd have to rewire everything.



The biggest upgrade after splitting the positive supplies would probably be constant current sources under the 6as7's instead of the 3K3 resistors. The more you isolate the cathode of the 6as7, the better off you'll be. A couple DN2540's, some adjustable cermet resistors, and a little heatsinking are the easiest way to start down the CCS road, though you can go totally crazy. But listen to the amp a lot with the resistors first before you try that, some people don't like it and you'll want to compare.

Glad it's working so well!

 

[sbelyo]

Quote:

Originally Posted by philodox Trust me this is not always the case.

This is true

What was the design you tried?

 

[sbelyo]

Quote:

Originally Posted by Rescue Toaster Hey sbelyo, nice work. Couple questions, you have no extra resistors in the power supply yet, right? What voltage do you get on top of the 6as7's? Close to 170v? What is the voltage on the cathode of the 6as7's? (ie how much current are they passing)

Thanks... I'm tempted not to touch it. No extra resistor in the power supply

I measured 158V at full load before C1
156V at full load at C1
141V at full load at C2

I didn't measure the voltage at the tube itself yet. What are the correct pins?
Quote:

Originally Posted by Rescue Toaster Drew a little picture for you of what I meant, though I think you got it. You could even do totally separate L & R star grounds, and run separate wires from the power supply star ground to each. But... I don't think it's a big issue and you'd have to rewire everything.

Thanks for the pic. This is definitely the next tweak

Quote:

Originally Posted by Rescue Toaster The biggest upgrade after splitting the positive supplies would probably be constant current sources under the 6as7's instead of the 3K3 resistors. The more you isolate the cathode of the 6as7, the better off you'll be. A couple DN2540's, some adjustable cermet resistors, and a little heatsinking are the easiest way to start down the CCS road, though you can go totally crazy. But listen to the amp a lot with the resistors first before you try that, some people don't like it and you'll want to compare. Glad it's working so well!

Thanks for the idea... I'll have to read up on that more so I understand it. It works way better then I expected so I'm gonna listen to it for a few weeks before I start tweaking

 

[Rescue Toaster]

Quote:

Originally Posted by sbelyo Thanks... I'm tempted not to touch it. No extra resistor in the power supply I measured 158V at full load before C1 156V at full load at C1 141V at full load at C2 I didn't measure the voltage at the tube itself yet. What are the correct pins?

Hmm, are you sure you don't have C1 & C2 backwards? Referring to the pic on headwize here. The voltage on the cap across the input tube should be lower than the cap across the 6AS7's. Initially you said you had 168 volts under full load? Now 158? It looks like you might not have enough voltage to spare to do what I'm suggesting. Maybe try 330's or even 220's instead of the 470's I suggested. 220's should be totally fine, 330's probably also. If you had to order 10 470's (they usually make you get 10) just use 2 paralleled each for a pair of 235 ohm resistors. I don't want you to drop your voltages too low. Really you can use those two 470's (or whatever) to tune in your amp to exactly 150v

 

[sbelyo]

Quote:

Originally Posted by Rescue Toaster Hmm, are you sure you don't have C1 & C2 backwards?

I don't think so, but I'll double check

Quote:

Originally Posted by Rescue Toaster Referring to the pic on headwize here. The voltage on the cap across the input tube should be lower than the cap across the 6AS7's. Initially you said you had 168 volts under full load? Now 158?

Actually when I measured the first time I just put a 3.3K 20 watt resistor across the B+. That should've drawn close to 60mA but the amp may draw more than that.
Quote:

Originally Posted by Rescue Toaster It looks like you might not have enough voltage to spare to do what I'm suggesting. Maybe try 330's or even 220's instead of the 470's I suggested. 220's should be totally fine, 330's probably also. If you had to order 10 470's (they usually make you get 10) just use 2 paralleled each for a pair of 235 ohm resistors. I don't want you to drop your voltages too low. Really you can use those two 470's (or whatever) to tune in your amp to exactly 150v

I usually protoboard this stuff first just to see if it works so I don't have to rip up all the wiring just to find out it's not gonna work. This was my thought when making the PSU on protoboard so I could swap it out easily. On my next order I'll toss in the parts

 

[philodox]

Quote:

Originally Posted by sbelyo What was the design you tried?

Sent you a PM.

 

[jbloudg20]

Quote:

Originally Posted by philodox Sent you a PM.

I'd be curious to know as well, if you don't mind.

 

[sbelyo]

Been tube rolling....

So far I like the 6AS7G over the 6080. The bass is ever so slightly better.

 

[Voodoochile]

Sharp looking amp! Nice job, sbelyo.

What's next on deck?

 

[sbelyo]

Quote:

Originally Posted by Voodoochile Sharp looking amp! Nice job, sbelyo. What's next on deck?

Thanks... I can do better, this was my first go at tubes and point to point wiring. Now that I understand how to space and place things my next one should be better.

Next is the Kurt Strain OTL amp with 12au7's and 6cg7's. I also have the tubes for a 6SN7 (I'm a sucker for octals) version. I just have to sell my PPA to gather the rest of the parts.

 

[Voodoochile]

Quote:

Originally Posted by sbelyo I just have to sell my PPA to gather the rest of the parts.

Such is life. I still have my PPA, but my original Ear+Purist HD is going to have to find another home soon.

Wouldn't it be nice to be rather wealthy, and just let your rigs pile up in some sort of conservatorial wing off your house? Each with it's own high end source. It would be like having a mini-meet set up at your house all the time.

 

[sbelyo]

Quote:

Originally Posted by Voodoochile Wouldn't it be nice to be rather wealthy, and just let your rigs pile up in some sort of conservatorial wing off your house? Each with it's own high end source. It would be like having a mini-meet set up at your house all the time.

That would be good...

It's a good hobby though.. I've learned a ton, and there's always someone looking to buy an amp somewhere.

 

[sbelyo]

I added another 100uf on the output. The overall result is good, I would say it finishes it off. That makes 320uf silmic II bypassed by 0.22uf solen

If building the amp I would go with 330uf or 470uf first off. The max voltage I saw at the caps were 80 Vdc. It is wise not to drop below 250V because things can fail and you wouldn't want the full B+ accross your head.

 

[sbelyo]

I figured I would let people know what long term listening is like with this amp....

This amp is sounding great. I would say it has 500 hours on it and I find myself using it more than my Dynahi....

I'm gathering parts for the 6SN7 Version of the strain OTL so watch for a new post in the next few weeks